<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    * {
        padding: 0;
        margin: 0;
        list-style-type: none;
    }

    #ul1 {
        width: 100%;
        display: flex;
    }
    li{
        height: 30px;
        flex: 1;
    }
    #ul1 li:nth-child(1){
        background-color: antiquewhite;
    }
    #ul1 li:nth-child(2){
    background-color: skyblue;
    }
    #ul1 li:nth-child(3){
    background-color: red;
    }
    #ul1 li:nth-child(4){
    background-color: green;
    }
    #ul1 li:nth-child(5){
    background-color: blue;
    }
</style>

<body>
    <ul id="ul1">
        <li>1</li>
        <li>11</li>
        <li>111</li>
        <li>1111</li>
        <li>11111</li>
    </ul>
</body>

</html>